Couple of buttercream related questions from a cake decorating novice

[TrickyBiscuits]

I love decorating cakes but it seems I'm woefully inadequate at it

The last time I made cupcakes I piped rose-style swirls on top of them and they looked lovely...for about 20 minutes before they collapsed! I'm guessing of course that the buttercream wasn't thick/dense enough for them to hold their shape whilst they set, but I felt that it was thick as I could get it before it wouldn't be pipe-able Could the problem be that I added a drop of lemon juice? It still appeared thick but does the lemon acid affect the butter? I don't suppose anyone has a good tried and tested recipe for buttercream I could use?

Also, if I want to use buttercream as a base for fondant on a cake, do I let the buttercream set first? Do I only use a tiny bit?

Thanks very much in advance

You might have had too much butter in there, which would have made the buttercream soften if it was warm in the room.

I use equal weights of butter and icing sugar, and usually add a splash of milk, a bit of lemon juice or a bit of vanilla extract. I beat it forever, I don't think you can over-mix buttercream! That makes it nice and light for piping.

That's about the extent of my knowledge I'm afraid!

I used to do equal weights of butter/alternative and icing sugar but lately I've had better results using a 3:1 ratio of icing sugar to fat.
The cream pipes and holds its shape well, although you need to pipe it at room temperature.

Yes, I'd use 3 or 2 parts icing sugar to one of butter. I don't think the lemon juice would have made much difference.
If you want really lovely shapes, it's a bit of a pain, but Swiss meringue buttercream is wonderful stuff
More about that here:
smittenkitchen.com/blog/2008/07/project-wedding-cake-swiss-buttercream/

Ah that's probably it then: I haven't been putting enough sugar in. See this is what happens when you randomly tip ingredients in together and hope for the best

Thanks very much everyone! I'll definitely try the Swiss meringue recipe once I've mastered some of the basics